Communications of audio information play an important role in multimedia applications, and Internet applications such as a music-on-demand service, music preview for online compact disk (CD) purchases, etc. To efficiently utilize bandwidth to communicate audio information, a perceptual audio coding (PAC) technique has been developed. For details on the PAC technique, one may refer to U.S. Pat. No. 5,285,498 issued Feb. 8, 1994 to Johnston; and U.S. Pat. No. 5,040,217 issued Aug. 13, 1991 to Brandenburg et al., both of which are hereby incorporated by reference. In accordance with such a PAC technique, each of a succession of time domain blocks of an audio signal representing audio information is coded in the frequency domain. Specifically, the frequency domain representation of each block is divided into coder bands, each of which is individually coded, based on psycho-acoustic criteria, in such a way that the audio information is significantly compressed, thereby requiring a smaller number of bits to represent the audio information than would be the case if the audio information were represented in a more simplistic digital format, such as the PCM format.
For example, in providing the aforementioned music-on-demand service, a server connected to the Internet may store PAC compressed versions of each available musical piece to serve client needs. Each version of the musical piece corresponds to a different connection speed at which a client, e.g., a personal computer (PC) having a modem, can afford to communicate over the Internet. The quality, or the lack of distortion, of the version of the musical piece increases with the connection speed corresponding thereto. Thus, for instance, if the server supports (a) a plain old telephone service (POTS) connection speed of about 28.8 kb/sec, (b) an integrated services digital network (ISDN) connection speed of about 64 kb/sec, and (c) a dual ISDN connection speed on the order of 100 kb/sec, three corresponding versions of the musical piece having the respective qualities need to be stored in the server. However, the storage of musical pieces in this manner is undesirably inefficient and occupies much memory space especially when a large number of musical pieces need to be made available.
In delivering the service to a client at a given connection speed, the server may packetize the corresponding audio information in the storage, and communicate the resulting packets through a packet switched network, e.g., the Internet. However, in the event that some of the packets are lost in transit because of imperfect network or channel conditions, which is likely, the quality of the received signal representative of a musical piece would be significantly degraded.
Accordingly, there exists needs for efficiently storing and distributing information at different rates, and effectively maintaining the minimum acceptable quality of the received signal despite imperfect network or channel conditions.